Abstract Classes

Utilities to deal with abstract base classes and virtual subclasses.

New in version 0.2.

class brownie.abstract.ABCMeta

On Python 2.6 this class is actually abc.ABCMeta, on versions lower than that it’s simply a dummy. Which makes implementing abstract classes easier if you want to support Python versions which don’t support class.__subclasscheck__() and class.__instancecheck__().

class brownie.abstract.VirtualSubclassMeta(name, bases, attributes)

A metaclass which allows you to easily define abstract super classes, simply inherit from this metaclass and set the virtual_superclasses attribute to an iterable:

>>> from brownie.abstract import ABCMeta, VirtualSubclassMeta
>>>
>>> class VirtualBaseClass(object):
...     __metaclass__ = ABCMeta
>>>
>>> class VirtualSubclass(object):
...     __metaclass__ = VirtualSubclassMeta
...
...     virtual_superclasses = (VirtualBaseClass, )
>>>
>>> issubclass(VirtualSubclass, VirtualBaseClass)
True

class brownie.abstract.AbstractClassMeta(name, bases, attributes)

A metaclass for abstract base classes which are also virtual subclasses.

Simply set virtual_subclasses to an iterable of classes your class is supposed to virtually inherit from:

>>> from brownie.abstract import ABCMeta, AbstractClassMeta, \
...                              VirtualSubclassMeta
>>> class Foo(object):
...     __metaclass__ = ABCMeta
>>>
>>> class Bar(object):
...     __metaclass__ = AbstractClassMeta
...
...     virtual_superclasses = (Foo, )
>>>
>>> class Baz(object):
...     __metaclass__ = VirtualSubclassMeta
...
...     virtual_superclasses = (Bar, )
>>>
>>> issubclass(Baz, Foo)
True
>>> issubclass(Baz, Bar)
True

Note

All classes could use AbstractClassMeta as __metaclass__ and the result would be the same, the usage here is just to demonstrate the specific problem which is solved.